Polyethylene is a versatile and inexpensive plastic that is used in the highest volume of any plastic. Polyethylene has toughness, near zero moisture absorption, excellent electrical insulating properties, low coefficient of friction, and is easily processed. Specialty grades of polyethylene include low density polyethylene (LDPE), medium density (MDPE), and many others. For example, LDPE is used in food packaging film, including stretch and shrink wrap; for plastic bags such as grocery bags, laundry and dry cleaning bags; for extruded wire and cable insulation; and for bottles, closures, and toys.
Polyethylene is not a high-performance plastic. Polyethylene, which is semi-crystalline, has a low glass transition temperature and crystalline melting point. Therefore it tends to lose its mechanical properties above its glass transition temperature. For example, polyethylene can have a low heat deflection temperature. Thus polyethylene has a low practical end use temperature. Some of the performance deficiencies of polyethylene can be addressed by the replacement of all of part of the polyethylene with polypropylene. However, polypropylene has poor UV stability, and UV stabilizers must be used for outdoor applications. Some of the performance deficiencies of polyethylene can also be addressed by the use of inorganic fillers. However the use of inorganic fillers leads to increases in specific gravity and adversely affects melt flow properties, elongation, and impact strength.
Poly(phenylene ether) (PPE) can be utilized as an organic filler for polyethylene and other polyolefins. Poly(phenylene ether) is a plastic having excellent water resistance, dimensional stability, and inherent flame retardancy, as well as high oxygen permeability and oxygen/nitrogen selectivity. Properties such as strength, flexural modulus, and heat deformation resistance of polyolefins can be improved by blending them with poly(phenylene ether)s, which serve as organic fillers, so that the compositions meet the requirements of various consumer products, for example plumbing fixtures, electrical boxes, and automotive parts. However, other properties, such as elongation, impact strength, and melt flow, can be adversely affected by blending poly(phenylene ether)s with polyolefins. Therefore, there remains a need for polyolefin molding compositions having increased heat deformation resistance, flexural modulus, and flame resistance, without sacrificing other physical properties. In particular, it is desirable that increased heat deformation resistance, flexural modulus, and flame resistance be obtained without adversely affecting elongation, impact strength, melt flow, density, and UV stability.